#define _CRT_SECURE_NO_WARNINGS 1
#include <stdio.h>
int main() {
	double sum = 0;
	int num = 0;
	for (num = 1; num <= 100; num++)
		if (num % 2 == 0)
			sum -= 1.0 / num;
		else sum += 1.0 / num;
	printf("%f\n", sum);

















	return 0;
}